A cage of this type is described in DE 3706013 A1. Cages of this type are manufactured from plastic. Typical examples of materials which are used for the manufacture of cages of this type are polyamides which are reinforced with glass or with carbon fibers (for example, PA66/GF). The cage has two side rings which are connected to one another by webs. One of the side rings is arranged on one side of the cage above the pitch circle and another of the side rings is arranged below the pitch circle. The side rings on cages of the generic type are also known as side rims. The side rims of the cage are provided with annular grooves, starting from the end sides.
Cages of the type under consideration are particularly difficult to design if they additionally have retaining lugs. Said retaining lugs are formed as a rule on one of the side rims and engage into a corresponding circumferential groove of one of the bearing rings of the tapered ball bearing. The cages, together with the balls and the corresponding bearing ring, are preassembled via the retaining lugs to form a self-contained structural unit, from which balls cannot fall during assembly in the other bearing ring of the tapered ball bearing. Retaining lugs of this type are also provided for axial path limitation of the cage in a bearing.
During assembly of the cage on the bearing ring, the retaining lugs are either compressed or extended elastically until the retaining lugs snap into a corresponding groove of the bearing ring. The wall thicknesses in the region of the transition of the retaining lugs into the cage therefore have to be of sufficiently stable dimensions, in order not to be deformed plastically permanently during assembly of the cage on or in the bearing ring. On the other hand, the retaining lugs have to be elastic enough, in order not to make assembly of the cage in the bearing difficult and in order to prevent damage to the cage or the retaining lugs. Therefore cages, the rims of which have relatively large cross sections, are normally advantageous for the stability of the cage. However, the assembly forces for pushing them, for example, onto an inner ring and expanding the retaining lugs in the process are relatively high. Moreover, the retaining lugs are easy to damage on account of the high assembly forces.
According to DE 3706013 A1, the annular grooves are provided in the side rims, in order to configure the wall thicknesses of the rims to be as thin as possible and in order to achieve uniform wall thickness in all regions of the side rims. Uniform wall thicknesses and wall thickness transitions are aimed for during injection molding of plastic parts, in order to avoid interruptions of the material flow/bubbles of the cage material in the cavities of the injection molding dies at the transition from thick to thin cross sections. Moreover, identical cooling speeds are achieved in all regions of the workpiece as a result of uniform wall thicknesses. Faults from undesired weakening in thin wall regions are also avoided by flow paths in cavities which are as short as possible with a relatively small injection cross section.
The thin-walled configuration is subject to limitations as a result of the requirements for high operating strength of the cage. If the cross sections of cages of this type are too small, it is to be feared that the cages with the retaining lugs which are mentioned in the beginning break during assembly of the bearing or exhibit permanent deformations. Incidentally, thin-walled plastic parts are extremely unstable after removal from the die and frequently lose their intended shape or geometry during subsequent cooling and during storage.